Of card materials to be selected for use, in particular PVC has proven useful. DE 30 48 736 A1 discloses for example a single-layer identity card of PVC dyed white with titanium dioxide. However, PVC is also preferably used in cards which consist of several layers. This material can be processed into foils which offer considerable advantages over other foil materials as the starting material for the individual layers. The individual layers can thus be laminated, i.e. interconnected under pressure and heat. Additives which influence or determine certain properties of the PVC foil can be incorporated very well in the material. For example one can produce both transparent layers and opaque layers. Furthermore this plastic can be mixed with pigments and other usual additives so that the material properties can be adjusted within wide limits, e.g. color, radiation absorption behavior and the like.
Multilayer identity cards of PVC have also been proposed which consist for example of a printed opaque card core and two transparent cover foils (DE 30 29 939 A1). Since all layers consist of the same plastic material they can be connected into a card laminate in a simple way.
However, PVC itself has the decisive drawback in terms of environmental acceptability that it can hardly be recycled. Disposal of the plastic furthermore causes considerable difficulties since hydrochloric acid arises during combustion and ultimate disposal of PVC. Furthermore PVC readily becomes brittle at low temperatures so that the card breaks easily.
To improve the mechanical properties and temperature stability of PVC cards, on the one hand, and reduce the quantity of PVC used, on the other, one has proposed producing high-grade cards from several layers of different materials.
EP 430 282 A2 thus discloses a card wherein the PVC cover layers and the PVC core layer of the card are each separated by a layer of thermoplastic polyurethane (TPU) so that the mechanical properties are improved. The PVC layers in such cards can also be replaced by other plastics, such as polyethylene or polycarbonate, without adversely affecting the mechanical properties of the card.
A drawback of such multilayer cards, however, is that the different plastics in the card compound can hardly be separated again on a large scale for recycling processes. At the end of the service life of the card only the crushed card laminate, i.e. a mixture of the plastics used, can be further treated in the recycling process, so that the card compound can only be processed into inferior plastic articles which cannot meet any high requirements with regard to color and mechanical properties.